The present invention relates to a type setting device and, more particularly, to a type setting device which permits a drive motor to be constantly rotated.
A printing mechanism for a miniaturized serial printer used for desk calculators or the like generally has a type wheel having a plurality of type elements on its circumferential surface and capable of being moved in the direction of a line to be printed. A mechanism for selecting a particular type element rotates the type wheel so as to set a desired type element in a printing position, and a printing hammer typically having a length equal to the entire line to be printed by the type wheel is supported pivotally and moved by a solenoid.
The type wheel is aligned in position along the line to be printed and rotated to allow a desired type element to be set in a printing position. Recording paper is inserted between the printing hammer and the ink-carrying type element and is pressed against the type element by the hammer to thereby print a character. The type wheel is then moved laterally so as to become aligned with the next place along the printing line, and a printing operation as described above is repeated. Printing operations are thereafter carried out in the same manner repeatedly to print one line of characters.
The type wheel is typically stopped when the recording paper is pressed against a type element by the hammer, so that thin characters or broken files do not occur. In this way, printed characters of a high quality can be obtained. This also allows the hammer to be simply controlled with respect to the timing of the drive of the type wheel.
In a conventional serial printer, the type wheel is directly connected to a shaft of a stepping motor, and the motor is driven by suitable pulses to select a particular type element. Accordingly, it is necessary that the motor be controlled with respect to its starting, rotation and stopping every time one character is to be printed. As a result, it takes a considerably long time to start and stop the motor so that high-speed printing cannot be carried out. Moreover, the motor control circuit is necessarily complicated.